The present invention relates generally to spark plugs for use with internal combustion engines, and more particularly to a spark plug having electrodes and spark gaps therebetween which define a three-dimensional volume.
Most internal combustion engines utilize a spark plug for initiating combustion of the air/fuel mixture in the combustion chamber. The spark produced by the spark plug will ignite the air fuel mixture local to the spark gap if it is within an acceptable range near the stoichiometric ratio for the particular fuel utilized. The probability that the mixture will be ignited will be reduced when the mixture within the gap is excessively fuel rich or fuel lean. The engine""s fuel delivery system will attempt to maintain the overall air/fuel ratio within an acceptable range. However, due to unavoidable inhomogeneity of the mixture within the combustion chamber, the probability of ignition of the mixture by a spark will vary spatially. If a spark is not produced in an optimal air/fuel region within the chamber, a misfire will occur, resulting in expulsion of the unburned air-fuel mixture from the combustion chamber without any production of power, which in turn results in increased emissions and decreased engine efficiency. This condition will be aggravated when the overall fuel/air ratio is fuel-lean; as in lean-burn engines, since this will tend to increase the number of excessively fuel-lean regions within the combustion chamber. Furthermore, the regions of optimal air/fuel ratio within the combustion chamber may change with time.
The probability of igniting the mixture can be increased by supplying a multiplicity of sparks within the combustion chamber each time ignition is required. This can be accomplished by employing two or more conventional single-gap spark plugs within each combustion chamber or employing a multiple-gap or multiple-electrode spark plug to produce more than one spark at a time. However, there are practical limits to the number of spark plugs that can be utilized in each combustion chamber, and there are subtle design issues for multiple-electrode spark plugs which must be considered in order to maximize their performance relative to conventional spark plugs.
The initial stage in the combustion of the air-fuel mixture is called the ignition delay period and is generally defined by the formation of a stable flame front from the spark. The spark ignites the mixture, producing a small ball of flame called the flame kernel. The flame kernel is small and unstable and may become extinguished if the conditions for combustion are not optimal, resulting in a misfire. The flame kernel grows and becomes more stable as it burns more of the mixture, eventually becoming a hollow sphere of flame known as a flame front. Because the amount of fuel burned versus time is an exponential function, the ignition delay period is usually a large fraction of the total combustion time, sometimes as much as 50%. Significant decreases in total combustion time can therefore be realized by decreasing the ignition delay time.
It is desirable to decrease combustion time because significant increases in thermodynamic efficiency of the combustion process can be made by decreasing the combustion time of the mixture resulting in improved fuel efficiency, increased power, and reduced emissions.
One of the best ways to reduce the ignition delay time is to produce a larger spark. This produces a more stable flame kernel, which will eventually become a stable lame front in less time than those formed via a smaller spark. Again, this is more beneficial for lean fuel/air ratios which cause longer ignition delay times. The size of a single spark, however, is limited by available ignition energy and geometric constraints of a standard, single gap spark plug.
It is therefore evident that there exists a need in the art for a spark plug which provides multiple sparks forming a three-dimensional volume for reducing combustion time and mitigating ignition misfires, increasing engine power and efficiency, and decreasing fuel consumption.
In accordance with the present invention, there is provided a spark plug for producing a plurality of sparks which define a three-dimensional volume in a combustion chamber of an internal combustion engine. The spark plug is provided with an insulative body having a support end. The spark plug is further provided with a central positive electrode which extends through the insulative body. The central positive electrode has a spark ignition end. The spark plug is further provided with a conductive outer shell which is disposed about the insulative body. The spark plug is further provided with at least two neutral electrodes which are attached to the support end of the insulative body. One of the neutral electrodes is adjacent to the spark ignition end of the central positive electrode and spaced apart therefrom to form a spark gap therebetween. Another one of the neutral electrodes is adjacent to the conductive outer shell and spaced apart therefrom to form a spark gap therebetween. The neutral electrodes being spaced apart from one another to form spark gaps between each other. The spark gaps thus defined in turn define a three-dimensional volume.
In practice, the spark plug of the present invention facilitates the formation of an electrical circuit. In this respect, electrical current may be applied to the central positive electrode and may flow to the spark ignition end thereof. Such current may continue to flow to the neutral electrodes by traversing the spark gaps therebetween in the form of a spark. The electrical circuit is completed as a spark traverses from a neutral electrode to the conductive outer shell which functions as a source of electrical ground.
Preferably, the central positive electrode defines a longitudinal axis and adjacent ones of the neutral electrodes being disposed radially progressively further away from the longitudinal axis of the central positive electrode. In addition, the central positive electrode has an electrical connection end and adjacent ones of the neutral electrodes are progressively further away from the spark ignition end of the central positive electrode generally towards the electrical connection end of the central positive electrode. In this respect, the spark ignition end of the central positive electrode and the neutral electrodes are configured along a generally spiral helix path so as to facilitate the formation of sparks across the respective spark gaps substantially along the spiral helix path.
As such, based on the foregoing, the present invention mitigates the inefficiencies and limitations associated with prior art spark plugs. The present invention is particularly adapted to facilitate the generation of a series of sparks which define a three-dimensional volume. In this respect, it is contemplated that the sparks may quickly merge so as to form a large flame front which reduces combustion time and mitigates ignition misfires, thereby facilitating an increase in engine power and efficiency and a decrease in fuel consumption and emission.
Accordingly, the present invention represents a significant advance in the art.